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Chapter 21
Amino Acids, Peptides, and Proteins
Important Terms
amino acid
an
a
-amino carboxylic acid. Naturally occurring amino acids have the l-configuration.
d-amino acid
the configuration of an amino acid drawn in a Fischer projection with the carboxyl
group on top, the hydrogen on the left, and the amino group on the right.
l-amino acid
the configuration of an amino acid drawn in a Fischer projection with the carboxyl
group on top, the hydrogen on the right, and the amino group on the left.
amino acid analyzer
an instrument that automates the ion-exchange separation of amino acids.
anion-exchange resin
a resin that binds anions.
antiparallel
B
-pleated sheet
a type of secondary structure in which the adjacent hydrogen-bonded polypeptide
chains in a
b
-pleated sheet run in opposite directions.
automated solid-phase
an automated technique that synthesizes a polypeptide (in the C-terminal to
peptide synthesis
N-terminal direction) while its C-terminal amino acid is attached to a solid support.
cation-exchange resin
a resin that binds cations.
coil conformation
the part of a protein that is highly ordered but not in an
a
-helix or
b
-pleated
(loop conformation)
sheet.
C-terminal amino acid
the terminal amino acid of a peptide (or protein); it has a free carboxyl group.
denaturation
the destruction of the highly organized secondary and tertiary structure of a protein.
dipeptide
two amino acids linked by an amide bond.
disulfide
a compound with an S—S bond.
disulfide bridge
a disulfide (S—S) bond formed by two cysteine residues in a polypeptide or protein.
Edman’s reagent
phenyl isothiocyanate; the reagent used to determine the N-terminal amino acid of
a polypeptide.
electrophoresis
a technique that separates amino acids on the basis of their pI values.
endopeptidase
an enzyme that hydrolyzes a peptide bond that is not at the end of a polypeptide chain.
essential amino acid
an amino acid that humans must obtain from their diet because they cannot synthe-
size it at all or cannot synthesize it in adequate amounts.